Installation

Kernel

Enabling USB requires to modify /mach_kernel.prelink on the AppleTV.
If this file isn't there yet, this means the system partition hasn't been forced to be mounted read/write yet.
Force it read/write with:

Is it safe to simply remove the USB drive from the AppleTV or do you need to first 'unmount' the drive?
--PatentBoy 18:27, 27 March 2008 (CET)

At the time you see the drive with diskutil, its partitions have not been mounted yet.
You have to mount them with the mount command.
Once you've done this, it is not safe to remove the drive without having issued an umount command.
Unix does not always directly update the changes on the harddisks: it can buffer the changes and update them when it finds time for it.
Removing a mounted drive can lead to have inconsistent data on it...